One widely used available test system is an oscilloscope. Generally an oscilloscope is an instrument which captures a waveform for a period of time and can then generate an image corresponding to the time domain waveform samples on a display of the oscilloscope. Additionally, the information captured by the oscilloscope can be stored on a storage device, and further processed to provide a wide range of measurement information. One of the challenges in using an oscilloscope is determining when to start, or trigger, the capturing or displaying of data. Frequently, the signal which is being measured using an oscilloscope is a periodic, or sporadic, type of signal where the voltage of interest occurs at different points in time, and for relatively short periods of time. Thus, one of the challenges in using an oscilloscope is determining when to trigger the capture or display of measurement data, because for relatively long stretches of time there can frequently be no information of interest.
In the past, some oscilloscopes were triggered based on the magnitude and the slope of an incoming measurement signal waveform. With the advent of higher speed oscilloscopes based on an array of moderate speed analog to digital converters (ADC) running in parallel, some of the previously used trigger techniques have been found to have significant limitations.
Some prior high speed oscilloscopes have used dedicated analog circuitry to generate trigger signals. The analog signal may come from the input signal directly, or in some cases the analog trigger can actually be reconstructed from a digital data stream (or a subset of the data stream) coming from the ADC. Generally, many of the prior implementations have been found to have significant limitations, particularly at high sampling rates and for higher frequency measurement signals.